Abstracts

Seizures triggered by photic stimulation are a common manifestation of both occipital epilepsies and idiopathic generalized epilepsies, especially juvenile myoclonic epilepsy (JME). Idiopathic photosensitive occipital epilepsy (IPOE) was described as a focal epilepsy with colourful elementary visual auras, often with prominent conscious tonic head and eye version; myoclonus is not feature. All seizures are induced by photic stimuli. JME is characterized by myoclonic jerks (MJ) and generalized tonic clonic seizures (GTCS) with photosensitivity occurring in 30% patients; visual auras are not recognized. JME is associated with generalized spike and wave (GSW) on EEG whilst IPOE has occipital spikes with or without GSW. Intermittent photic stimulation (IPS) may produce GSW in both; in IPOE occipital spikes are seen. We describe four families with overlap between JME and IPOE.
Four families were identified where two or more affected individuals had visual auras and electro-clinical features of an idiopathic epilepsy. Available living affected family members underwent detailed electro-clinical assessment. A 21-channel EEG including IPS and hyperventilation was performed. An additional Oz electrode was used in some cases. International classification was used to classify seizure types.
There were 12 affected individuals in four families of which 11 were female. Clinical onset was 8-21 years (mean 11y). Ten patients had visual auras including coloured circles or bright flashes of light; six with conscious head version. Five also experienced MJ. Of the remaining individuals, one had MJ and occipital spikes; the other had GTCS without visual aura or MJ. Of the 10 individuals with visual auras, 7 had non-photic induced GTCS. Of 10 patients with EEG studies, 8 had GSW and 6 had occipital spikes. All had photosensitivity with GSW and 4 had photic-induced occipital spikes.
There is overlap between the clusters of clinical features used to diagnose IPOE and JME. Half of the affected individuals with visual aura had MJ; the former is characteristic of IPOE and the latter of JME. Importantly, visual aura is not regarded as part of JME, nor myoclonus part of IPOE but our data emphasize that these symptoms may occur in both disorders. Moreover, two thirds of individuals with visual aura had spontaneous GTCS; the latter feature is not described in IPOE.
Understanding the genetic basis of these disorders must account for the striking female predominance, the variable phenotypes associated with photosensitivity and the overlap of clinical features classically regarded as distinguishing focal and generalized syndromes. JME with photosensitivity and IPOE are clinically useful entities but these family data suggest more clinical overlap than previously appreciated. This is probably due to shared genetic determinants in their complex genetic architecture.
[Supported by: National Health and Medical Reseach Council]